In the dental treatments, it is necessary to bond treatment restorative materials to dentin or restorative materials. Important properties of adhesive compositions used for adhesion bonding are, for example, adhesion properties enough for withstanding oral cavity conditions, mechanical properties (e.g., flexibility) of cured products and favorable workability (e.g., proper setting time (curing time) and working time), capable of coping with applied cases.
It has been confirmed from the long-term clinical use that adhesives using as a polymerization initiator a partial oxide of tributylborane (TBB-O) that is an organoboron compound, e.g., a methyl methacrylate (MMA)/4-methacryloyloxyethyltrimellitic anhydride (4-META/partial oxide of tributylborane (TBB-O)/polymethyl methacrylate (PMMA) adhesive resin, not only have excellent adhesion properties but also are less bio-harmful. Such adhesive resins, however, have relatively low curing rate, and it has been pointed out that a relatively long period of time is necessary before the resins exhibit satisfactory adhesion performance, so that shortening of the setting time has been desired. However, it cannot be said that the shorter the setting time is, the better the dental adhesive compositions are, and it is preferable that the compositions are cured rapidly after the elapse of working time necessary for the dental treatment.
The present inventor has found that by the use of a polymerization initiation system comprising an organoboron compound and an appropriately small amount of a photopolymerization initiator, the curing rate can be controlled without exerting evil influences on the adhesion properties of an adhesive composition, and he has already applied for patent. This application has been already laid open (Japanese Patent Laid-Open Publication No. 110913/1997).
In the adoption of this polymerization system, however, an additional operation that light energy must be given by a certain means is required in order to control the curing rate by the use of an appropriately small amount of a photopolymerization initiator.
Under such circumstances, a basic solution to provide favorable workability with a proper setting time has been desired in the field of dental treatments.
The present inventor has studied such requirements as mentioned above, and as a result, he has found that by the addition of a small amount of a polyfunctional polymerizable monomer which is an ester compound of a polyhydric alcohol of 3 to 6 carbon atoms and plural (meth)acrylic acids and has 1 to 2 hydroxyl groups to a composition, the curing rate can be remarkably enhanced with rarely affecting adhesion properties of the composition, properties of a cured product and working time. Based on the finding, the present invention has been accomplished.
Patent document 1: Japanese Patent Laid-Open Publication No. 110913/1997